Datasheet

DocID024275 Rev 2 25/29
AN4260 Test equipment and measurement of efficiency and light load performance
Figure 39. Switch in position 1 - setting for standby measurements
In the case of high UUT input current (i.e. for measurements in heavy load conditions), the
voltage drop can be relevant compared to the UUT real input voltage. If this is the case, the
switch in Figure 38 can be changed to position 2 (see simplified scheme of Figure 40) where
the UUT input voltage is measured directly at the UUT input terminal and the input current
does not affect the measured input voltage.
Figure 40. Switch in position 2 - setting for efficiency measurements
On the other hand, the position of Figure 40 may introduce a relevant error during light load
measurements, when the UUT input current is low and the leakage current inside the
voltmeter itself (which is not an ideal instrument and doesn't have infinite input resistance) is
not negligible. This is the reason why it is recommended the setting of Figure 39 to be used
for light load measurements and Figure 40 for heavy load measurements.
If it is not clear which measurement scheme has the lesser effect on the result, try with both
and register the lower input power value.
As noted in IEC 62301, instantaneous measurements are appropriate when power readings
are stable. The UUT is operated at 100% of nameplate output current for at least 30 minutes
(warm-up period) immediately prior to conducting efficiency measurements.
V
+
-
A
~
AC
SOURCE
UUT
U.U.T.
AC
INPUT
Voltmeter
Ammeter
Wattmeter
AM16663v1
V
+
-
~
AC
SOURCE
UUT
U.U.T.
AC
INPUT
Voltmeter
Ammeter
A
Wattmeter
AM16664v1